This relates generally to electronic devices, and, more particularly, to electronic devices with electronic compasses.
Electronic devices such as cellular telephones may contain electronic compasses. An electronic compass includes magnetic sensors that detect the Earth's magnetic field. Compass readings may be used to provide orientation information to a navigation application or to other programs that use magnetic sensor data.
The magnetic sensors in electronic compasses may be formed from thin-film sensor structures. Magnetic flux concentrators are used to guide and amplify ambient magnetic fields, thereby enhancing the ability of thin-film sensors to detect weak fields such as the Earth's magnetic field. The magnetic flux concentrators are formed from soft magnetic materials.
Magnetic structures in a magnetic sensor such as the magnetic materials in a magnetic flux concentrator can become magnetized upon exposure to magnetic fields. For example, a magnetic flux concentrator may become magnetized when an external magnet or other source of a large external magnetic field is brought into the vicinity of the magnetic flux concentrator. The magnetization of a flux concentrator that has been exposed to magnetic fields in this way will relax to a remnant state upon removal of the external magnetic field. A remnant state will typically be characterized by a complex pattern of magnetic domains. This pattern of magnetic domains can give rise to a leakage flux that creates an undesired offset in the electronic compass. The offset can introduce inaccuracies in magnetic field readings and can limit the dynamic range of the electronic compass.
In some compass designs, magnetic flux concentrators have shapes that cause the compass to be more sensitive to magnetic fields with one angular orientation than another. If care is not taken, this angular sensitivity can give rise to inaccuracies in magnetic field readings.
It would therefore be desirable to be able to provide improved flux concentrators for magnetic compasses.